1. Field of the Invention
The present invention relates to a method of manufacturing an envelope used for an image display device and a method of manufacturing an electron beam apparatus that emits electrons and is used therefor.
2. Related Background Art
Up to now, two types of devices, namely, a hot cathode device and a cold cathode device have been known as electron-emitting devices in the electron beam apparatus used for the image display device, for example.
With respect to the cold cathode device of the two types, one disclosed in, for example, M. I. Elinson, Radio Eng. Electron Phys., 10, p.1290 (1965) and another one described later have been known as surface conduction electron-emitting devices. In addition, a field emission type device (hereinafter referred to as FE-type device), a metal/insulating-layer/metal type device (hereinafter referred to as MIM type device), and the like have been known.
The surface conduction electron-emitting device utilizes a phenomenon that electron emission is produced by allowing a current to flow into a thin film of a small area, which is formed on a substrate, in a direction parallel to the surface of the thin film.
Of image display devices using the above-mentioned electron-emitting devices, a flat display device which is thin is space-saving and light. Accordingly, the flat display device is focused as a substitute for a cathode ray tube display device.
FIG. 8 is a perspective view showing an example of a display panel unit composing a flat image display device. In FIG. 8, a portion of the display panel is cut to show an internal structure.
The flat image display device has a structure in which a rear plate 115 above which a plurality of cold cathode devices 112 are formed and a face plate 117 on which a fluorescent film 118 as a light emitting material is formed are opposed to each other through a structural support member 120 which is a space defining member (which is called a spacer or a rib). An airtight envelope that maintains the inner portion of the display panel in a vacuum is composed of the rear plate 115, a side wall 116, and the face plate 117. A substrate 111 is fixed onto the rear plate 115. The plurality of cold cathode devices 112 are formed on the substrate 111. In addition, a metal back 19 which is known in a CRT field is provided on the surface of the fluorescent film 118 on the rear plate 115 side.
Also, the inner portion of the above-mentioned airtight envelope is maintained at the degree of vacuum of about 10−6 [Torr]. In the case where a display area of the image display device increases, it is necessary to use a method of preventing a deformation or a breakage with respect to the rear plate 115 and the face plate 117, resulting from a pressure difference between the inside and the outside of the airtight envelope. In the case of adopting a method of thickening the rear plate 115 and the face plate 117, the weight of the image display device increases. In addition, when a screen is viewed from an oblique direction, a distortion of an image and a parallax are caused. In contrast to this, the spacers 120, each of which is made of a relatively thin glass plate and resistant to an atmospheric pressure are provided. A method of assembling the spacers 120 is described in, for example, U.S. Pat. No. 6,278,066 (WO98/28774, Japanese Patent Application Laid-Open No. 2000-510282), EP 690472 A (Japanese Patent Application Laid-Open No. H08-180821), and EP 405262 A (Japanese Patent Application Laid-Open No. H03-049135). Accordingly, an interval between the rear plate 115 and the face plate 117 on which the fluorescent film 118 is formed is generally kept on the order of submillimeter or to several millimeters. As described above, the inner portion of the airtight envelope is maintained at a high vacuum.
Also, the spacer 120 should not affect significantly a trajectory of an electron flying between the rear plate 115 and the face plate 117. Charging of the spacer 120 is one of causes which affect the electron trajectory. It is considered that a part of electrons emitted from an electron source or electrons reflected by the face plate 117 are incident in the spacer 120 and a secondary electron is emitted from the spacer 120, or ions ionized by collision of the electrons deposit on the surface of the spacer 120, with the result that the charging of the spacer 120 occurs.
In the case in which the spacer 120 is charged positively, since the electrons flying in the vicinity of the spacer 120 are attracted to the spacer, distortion occurs on a displayed image in the vicinity of the spacer 120. Such an influence of the charging becomes more conspicuous in accordance with increase in a space between the rear plate 115 and the face plate 117.
As a method of controlling charging in general, there is a method of removing charges by giving conductivity to a charged surface and causing a slight amount of electric current to flow to the spacer. The concept of this method is applied to the spacer 120, and EP 690472 A discloses a technique for coating a surface of the spacer 120 with a semiconductive film.
In addition, EP 405262 A discloses a technique for coating the surface of the spacer 120 with a PdO glass material.
In addition, breakage of the spacer 120 due to connection failure or concentration of electric currents can be prevented by applying an electric field to the above-mentioned coating material uniformly through the formation of an electrode in a contact surface of the spacer 120 with the face plate 115 and the rear plate 117.
In the image display device using the display panel described above, when voltages are applied to the respective cold cathode devices 112 through external envelope terminals Dx1 to Dxm of row-directional wirings 113 and external envelope terminals Dy1 to Dyn of column-directional wirings 114, electrons are emitted from the respective cold cathode devices 112. Simultaneously with this, a high voltage of several hundred volts to several kilovolts is applied to the metal back 119 through an external envelope terminal Hv to accelerate the emitted electrons, so that the electrons collide with the inside surface of the face plate 117. Thus, respective color phosphors composing the fluorescent film 118 are excited to emit lights, thereby displaying an image.
In the display panel of the image display device which is described in the conventional example, a plurality of spacers are arranged according to a display area of the display panel, a thickness of the rear plate, and a thickness of the face plate. However, in the case where the display area increases, the number of spacers increases and a time required to arrange the spacers on the display panel in a assembling process lengthens, so that a cost is increased. In addition, the degree of influence of a yield of the spacer in the assembly on a yield of the display panel increases and this causes an increase in a cost.
Further, in the case where the spacers are located outside a non-light-emitting region of the face plate because the assembly accuracy of the spacers is insufficient, a display image is influenced by the spacers, thereby making it difficult to display a high quality image. In addition, even if the spacers are located inside the non-light-emitting region, in the case where the spacers are misaligned because the assembly accuracy is insufficient, the spacers influences an electron beam trajectory, thereby distorting an image in some cases. In particular, this phenomenon is markedly exhibited in the case where the spacers are charged.